Phoenix performance issues with API

I’m using Phoenix to build a simple API that takes an HTTP request (JSON) and add the IP and user-agent to it and then insert it in MongoDB

 def imp(conn, params) do
    params=Map.put(params,"ip",conn.remote_ip |> Tuple.to_list |> Enum.join("."))
    params=Map.put(params,"ua",get_req_header(conn, "user-agent"))
    Mongo.insert_one(:mongo, "impression", params)
    json(conn,  %{})
  end

and it worked well, but what really is surprising is the performance, I have implemented the same function using NodeJS and this was the responses time of both:

                 Node     Phoenix 
#1             237 ms       4s
#2             65   ms      571ms
#3             30   ms     575ms
#4             33   ms     581ms
#5             27   ms     577ms
#6             30   ms     571ms
#7             31   ms     567ms

I have read about phoenix performance and how it should respond in microseconds time.

I thought that dealing with MongoDB is the issue, so I delete the insertion code but I still get 953ms response time (the first time) and 89ms, 350ms, 69ms the other times

so why my phoenix app is not that fast?

Note: I’m using Windows and Postman